The Washington Post covered the oral argument here:
Almost immediately Wednesday, questions from the bench centered on whether location information from cellphones is any different than records of banking transactions or landline phone calls.
Defense attorney Meghan S. Skelton said the government had essentially tracked the defendants’ every move, equating cellphone location data to “dragnet surveillance.” Maryland U.S. Attorney Rod J. Rosenstein countered that the information gleaned from cell towers was imprecise, unobtrusive and created by the wireless provider — not the government.
A divided three-judge panel of the court ruled in August that accessing the location information without a warrant for an “extended period” is unconstitutional because it allows law enforcement to trace a person’s daily travels and activities across public and private spaces.